Printing systems such as copiers, printers, facsimile devices or other systems having a print engine for creating visual images, graphics, texts, etc. on a page or other printable medium typically include various media feeding systems for introducing original image media or printable media into the system. Examples include thermal transfer printers. Typically, a thermal transfer printer is a printer which prints on media by melting a coating of ribbon so that it stays glued to the media on which the print is applied. It contrasts with direct thermal printing where no ribbon is present in the process. Typically, thermal transfer printers comprise a supply spindle operable for supplying a media web and ribbon, a print station, and a take up spindle. New ribbon and media is fed from the supply spindle to the print station for printing and then the ribbon is wound up by the take up spindle while the media is exited from the print station. As the ribbon exits the print station it is rewound on the take up spindle. Over the course of operation, the new ribbon on the supply spindle gradually decreases in radius while the used ribbon on the take up spindle gradually increases in radius.
Thermal transfer ribbons are supplied either coated side in or coated side out. In locations where these printers are used, it is common to have both types of ribbons. Ribbons wound coated side in rotate counter-clockwise during movement in the process direction, whereas ribbons wound coated side out rotate clockwise during movement in the process direction. Further, the ribbons come in various widths and in various ink compositions such has wax, wax/resin, or resin. For optimal print quality and reliable operation, it is desirable to be able to maintain a constant tension on the segment of ribbon being fed from the supply spindle to the print station and the segment from the print station to the take up spindle. It is also desirable to match the tension level with the ribbon width and composition.
A person of ordinary skill in the art will appreciate that the tension on the segment of ribbon between the supply spindle and the print station is generated by the print station pulling the ribbon and the supply spindle resisting this movement by applying force in the opposite direction. Conversely, the tension on the segment of the ribbon between the print station and the take up spindle is generated by the print station metering the ribbon at a fixed rate while the take up spindle is pulling the ribbon at an increased forced level in the same direction.
Referring now to FIG. 1, an exemplary conventional system 10 used in thermal transfer printers is shown. As shown, a supply spindle 12 is provided and feeds or supplies new/unused ribbon 14 with a coated side in configuration. The unused ribbon 14 is fed or supplied through a print station 16 where ink is deposited upon a media (not shown) which passes through a media feed path. Upon printing, used ribbon 18 is fed to a take up spindle 20 and wound about the same. Tensile forces (F) are placed upon both the unused ribbon 14 and the used ribbon 18. The tension or force on the ribbon is defined by the following equation:F=T/r 
where: F=torque/radius;                T=torque applied by the spindle; and        r=radius of the ribbon.As shown in FIG. 1, if the spindle torque is constant, the force (F) on the ribbon is directly proportional to the ribbon radius on the spindle. For the supply spindle 12, as the new ribbon 14 is used and the radius decreases, the force (F) on the ribbon 14 will decrease. For the take up spindle 20, as the radius of the used ribbon 18 increases, the force (F) on the ribbon 18 increases.        
Conventional thermal transfer printers have attempted to provide a constant tension on the ribbons by using mechanical systems of springs and clutches to exert a constant torque on each of the supply and take up spindles. However, during operation, the tension on the ribbons varies due to the fluctuation of radius of each spindle. Further, due to the mechanical nature of the conventional systems, coated side in and coated side out ribbons are not supportable absent reconfiguration of the system.
It would therefore be desirable to provide a system or device which continuously adjusts spindle torque to maintain a constant ribbon tension as the radius varies without the need for a mechanical system of springs and clutches. It would also be desirable to provide a device which independently controls the supply and take up ribbon segments tension. It would also be desirable to provide a system or device which allows for the automatic selection of ribbon tensions for optimal performance based upon ribbon width and type. It would also be desirable to provide a system or device which allows for the use of coated side in or coated side out ribbons without the necessity of system reconfiguration. Finally, it would be desirable to provide a system or device which monitors, detects, reports and controls the operation of both the supply and take up spindles during a printing operation, thereby providing for a constant ribbon tension in either a steady or dynamic state and during forward to backwards feed.